The present invention relates generally to a system and a method for measuring flow of a liquid. More specifically, the present invention relates to a non-invasive system and a method for measuring liquid flow driven by a flexible diaphragm, membrane pump, bellows, or piston.
Peritoneal dialysis (PD) is a generally known system requiring periodic infusion of sterile aqueous solutions into a peritoneal cavity of a patient. The infused solution is generally known as a peritoneal dialysis solution or dialysate.
Many types or forms of peritoneal dialysis are generally known, such as Continuous Ambulatory Peritoneal Dialysis (CAPD), Continuously Cycling Peritoneal Dialysis (CCPD), Automated Peritoneal Dialysis (APD), Intermittent Peritoneal Dialysis (IPD) and Tidal Peritoneal Dialysis (TPD).
In continuous ambulatory peritoneal dialysis (CAPD), a patient performs the dialysis manually about four times a day. During CAPD, the patient drains spent peritoneal dialysis solution from his peritoneal cavity. The patient then infuses fresh peritoneal dialysis solution into his peritoneal cavity. The drain and fill up procedure usually takes approximately one hour.
Automated peritoneal dialysis (APD) uses a machine, called a cycler, to automatically infuse, dwell, and drain peritoneal dialysis solution to and from the patient's peritoneal cavity. APD can be performed at night while the patient is asleep freeing the patient from day-to-day demands of CAPD during his waking and working hours.
APD typically lasts for several hours beginning with an initial drain cycle to empty the peritoneal cavity of spent dialysate. The APD sequence proceeds through a succession of fill, dwell and drain phases which follow one after the other. Each fill/dwell/drain sequence is called a cycle.
During the fill phase, the cycler transfers a predetermined volume of fresh, warm dialysate into the peritoneal cavity of the patient. The dialysate remains within the peritoneal cavity for a time period. During the drain phase, the cycler removes the spent dialysate from the peritoneal cavity. The number of fill/dwell/drain cycles that are required during a given APD session depends upon the total volume of dialysate prescribed for the patient's APD regime.
Continuously cycling peritoneal dialysis (CCPD) is one commonly used APD method. During each fill/dwell/drain phase of CCPD, the cycler infuses a prescribed volume of dialysate. After a prescribed dwell period, the cycler completely drains the liquid volume from the patient, leaving the peritoneal cavity empty. Typically, CCPD employs six fill/dwell/drain cycles to achieve a prescribed therapy volume.
After the last prescribed fill/dwell/drain cycle in CCPD, the cycler infuses a final fill volume. The final fill volume dwells in the patient through the day. The final fill volume is drained at the outside of the next CCPD session in the evening. The final fill volume can contain a different concentration of dextrose than the fill volume of the successor CCPD fill/dwell/drain fill cycles the cycler provides.
Intermittent peritoneal dialysis (IPD) is another form of APD. IPD is typically used in acute situations when a patient suddenly enters dialysis therapy. IPD can also be used when a patient requires IPD, but cannot undertake the responsibilities of CCPD. IPD involves a series of fill/dwell/drain cycles. The cycles in IPD are typically closer in time than in CCPD. In addition, IPD does not include a final fill phase. Rather, the patient's peritoneal cavity is left free of dialysate in-between APD therapy sessions.
Tidal peritoneal dialysis (TPD) is another form of APD. TPD includes a series of fill/dwell/drain cycles. Unlike CCPD, TPD does not completely drain dialysate from the peritoneal cavity during each drain phase. Instead, TPD establishes a base volume during the first fill phase and drains only a portion of the volume during the first drain phase. Subsequent fill/dwell/drain cycles infuse then drain a replacement volume on top of the base volume, except for the last drain phase. The last drain phase removes all dialysate from the peritoneal cavity.
Measurement of flow rate or other parameters of a liquid, either invasively or non-invasively is, of course, generally known. Peritoneal dialysis requires a technique for measuring flow rate that does not compromise sterility. Typically, the technique employed for such measurements is non-invasive. One common technique for non-invasively measuring flow rate in peritoneal dialysis is by differentiation of weight measurements. This technique uses a load cell which supports the supply bag and the drain bag to monitor weight differentials therebetween and to calculate rate therefrom. Such a technique enables one to derive instantaneous volume measurement.
In some applications or environments, however, instantaneous flow rate of a liquid must be determined within a sterile disposable without the use of gravity dependent weight measurements. In such environments, such as peritoneal dialysis procedures implementing a cassette-based system including a flexible diaphragm pump, a non-invasive technique is required for measuring and/or constantly monitoring flow rate going to or coming from a patient.
A need, therefore, exists for a system and a method for non-invasively measuring flow of a liquid driven by a flexible diaphragm or membrane pump to determine instantaneous flow rate and measurements derived therefrom.